Latest release (2.8.0) on Windows.
As you can see, I want to use the fontface on the right, and it works only if I don’t use images for the slider. The left slider has images and for some reason the font stays at this default one (Everything else works and every other font appears changed, at least from what I tested)
Knob Slider font does not change if using images
By the way you should download the latest beta release there is a post on the main forum page showing how to do this. There have been many improvements since the version you are using.